Methods for depositing viscous material on a substrate with a combination stencil printer and dispenser

ABSTRACT

A method of depositing viscous material on a substrate includes positioning the substrate in a print position, performing a print operation on the substrate with a print head and a stencil to deposit viscous material on the substrate, and inspecting the substrate with a vision system to detect a defect with the deposit of viscous material on the substrate. The method further includes, in the event of a defect, re-working the substrate by depositing viscous material on the substrate with a dispenser attached to a cleaning assembly, the stencil, or an independent gantry to correct the defect.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to U.S. patent application Ser. No. 12/963,448entitled COMBINATION STENCIL PRINTER AND DISPENSER AND RELATED METHODS,by Dennis G. Doyle, filed on even date herewith, U.S. patent applicationSer. No. 12/963,453 entitled COMBINATION STENCIL PRINTER AND DISPENSERAND RELATED METHODS, by Dennis G. Doyle, filed on even date herewith,and U.S. patent application Ser. No. 12/963,454 entitled COMBINATIONSTENCIL PRINTER AND DISPENSER AND RELATED METHODS, by Dennis G. Doyle,filed on even date herewith. All of these related applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of Disclosure

This disclosure relates generally to methods and apparatus for printingand dispensing viscous material, such as solder paste, onto a substrate,such as a printed circuit board, and more particularly to a combinationstencil printer and dispenser and related methods of printing anddispensing.

2. Discussion of Related Art

In a typical surface-mount circuit board manufacturing operation, astencil printer is used to print solder paste onto a printed circuitboard. A circuit board, broadly referred to as an electronic substrate,having a pattern of pads or some other conductive surface onto whichsolder paste will be deposited, is automatically fed into the stencilprinter. One or more small holes or marks on the circuit board, calledfiducials, is used to align the circuit board with the stencil or screenof the stencil printer prior to the printing of solder paste onto thecircuit board. The fiducials serve as reference points when aligning acircuit board to the stencil. Once a circuit board has been aligned withthe stencil in the printer, the circuit board is raised to the stencilby a substrate support, e.g., a table having pins or other work holders.Solder paste is then dispensed by moving a wiper blade or squeegeeacross the stencil to force the solder paste through apertures formed inthe stencil and onto the board. As the squeegee is moved across thestencil, the solder paste tends to roll in front of the blade, whichdesirably causes mixing and shearing of the solder paste so as to attaina desired viscosity to facilitate filling of the apertures in the screenor stencil. The solder paste is typically dispensed onto the stencilfrom a standard solder paste supply cartridge. After the printoperation, the board is then released, lowered away from the stencil,and transported to another station within the printed circuit boardfabrication line. Specifically, the stencil is separated from the boardand the adhesion between the board and the solder paste causes most ofthe material to stay on the board. Material left on the surface of thestencil is removed in a cleaning process before additional circuitboards are printed. In some applications, a cleaning assembly is movedunder the stationary stencil and excess material is wiped off of thestencil as the cleaning assembly is moved. In another application, thestencil is moved over the stationary cleaning assembly to clean theunderneath of the stencil.

The manufacturing of circuit boards involves many processes, one ofwhich is the screen printing of solder paste (or other adhesives ormaterials) on the surface of a circuit board with the stencil printer sothat electronic components can thereafter be deposited onto the board,which is described above. Another process is to dispense metered amountsof materials (liquid or paste) for a variety of applications with aseparate dispenser. One such application is the assembly of integratedcircuit chips and other electronic components onto circuit boardsubstrates. In this application, automated dispensing systems are usedfor dispensing dots of liquid epoxy or solder paste, or some otherrelated material, onto circuit boards. Automated dispensing systems arealso used for dispensing lines of underfill materials and encapsulents,which mechanically secure components to the circuit board. Underfillmaterials and encapsulents are used to improve the mechanical andenvironmental characteristics of the assembly. Another application is todispense very small amounts or dots onto a circuit board. Others includea syringe that utilizes pressure to dispense material from the syringe.In one system capable of dispensing dots of material, a dispensing pumputilizes a rotating auger having a helical groove to force material outof a nozzle and onto a circuit board. Yet another application is todispense dots of material by using a fetter.

Another process in the printing of circuit boards involves inspection ofthe boards after solder paste has been deposited on the surface of theboards. Inspecting the boards is important for determining that cleanelectrical connections can be made. An excess of solder paste can leadto shorts, while too little solder paste in appropriate positions canprevent electrical contact. Generally, in a stencil printer, a visioninspection system is employed to provide a two-dimensional or athree-dimensional inspection of the solder paste on the board.

Stencil printers typically contain an individual personal computer or“PC” and the only standard level of communication to adjacent pieces ofequipment is through an established protocol. For example, a printedcircuit board fabrication line may include one or more pieces ofequipment, such as stencil printers, dispensers, pick-and-placemachines, reflow ovens, wave soldering machines and/or inspectionmachines. Typically, process lines including stencil printers andplacement machines are operated by a pull system with the placementmachines controlling the introduction of product into different piecesof equipment in the production line. This is typically done in anattempt to maximize cycle time performance, primarily of the placementequipment. The production line is usually designed around the placementmachines. The placement machines are typically the more expensiveequipment in the production line, and so effort is made to keep themoperating at maximum capacity. Errors discovered in the printing processmay require manual intervention to rectify, which can impact the flow ofmaterials into the placement system, decreasing the utilization of theplacement system.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present disclosure is directed to a combinationstencil printer and dispenser for depositing viscous material on asubstrate. In one embodiment, the combination stencil printer anddispenser includes a frame, a stencil coupled to the frame, a substratesupport coupled to the frame to support a substrate in a print position,and a print head coupled to the frame to deposit and print viscousmaterial over the stencil. The print head is configured to move acrossthe stencil. The combination stencil printer and dispenser furtherincludes a cleaning assembly coupled to the frame to wipe excess viscousmaterial from a bottom surface of the stencil. The cleaning assemblyincludes a wiper assembly and a movement mechanism coupled to the frameand the wiper assembly to move the wiper assembly across the stencil ina first direction. The combination stencil printer and dispenser furtherincludes a dispenser coupled to the cleaning assembly to dispenseviscous material on the substrate when the substrate is in the printposition.

Embodiments of the combination stencil printer and dispenser includeproviding the dispenser with a dispensing unit secured to a frame memberof the wiper assembly by a bracket. The bracket of the dispenser iscoupled to a dispenser movement mechanism to move the dispenser withrespect to the frame member of the wiper assembly in a second directionthat is perpendicular to the first direction. The dispenser movementmechanism includes a linear bearing mounted on the frame member of thewiper assembly with the bracket being configured to ride along thelinear bearing. The dispenser movement mechanism further includes a ballscrew coupled to the bracket and configured to drive the movement of thebracket along the linear bearing. The dispenser movement mechanismfurther includes a motor coupled to the ball screw and configured todrive the rotation of the ball screw. In a certain embodiment, thedispenser includes another dispensing unit supported by the bracket. Inanother embodiment, the dispenser includes a mounting block coupled to aframe member of the wiper assembly and at least one dispensing unitsupported by the mounting block and in fluid communication with at leastone viscous material supply. The dispensing unit is configured todispense viscous material delivered by the at least one viscous materialsupply. The dispenser further includes at least one motor supported bythe mounting block and coupled to the at least one dispensing unit and asensor configured to detect a distance of the at least one dispensingunit to the substrate. The movement mechanism of the cleaning assemblyincludes a pair of rail members secured to the frame and a belt andpulley drive mechanism. A controller is provided to control theoperation of the combination stencil printer and dispenser.

Another embodiment of the present disclosure is directed to a method ofdepositing viscous material on a substrate. In a particular embodiment,the method comprises: positioning the substrate in a print position;performing a print operation on the substrate with a print head and astencil to deposit viscous material on the substrate; and depositingviscous material on the substrate with a dispenser attached to acleaning assembly.

Embodiments of the method include imaging fiducials associated with thesubstrate and aligning the substrate with the stencil when positioningthe substrate in the print position. The method further includesdelivering the substrate to the substrate support prior to positioningthe substrate in the print position, cleaning a bottom surface of thestencil with the cleaning assembly, and/or inspecting the substrate witha vision system to detect a defect with the deposit of viscous materialon the substrate. Inspecting the substrate with the vision systemincludes moving the vision system over the substrate with a visionsystem gantry under the control of a controller. Depositing viscousmaterial on the substrate with the dispenser is performed afterinspecting the substrate with the vision system to detect a defect. Thedispenser is configured to fix the defect.

Yet another aspect of the present disclosure is directed to acombination stencil printer and dispenser including a frame and astencil coupled to the frame by a stencil shuttle configured to supportand move the stencil in a first direction between a print position inwhich the stencil is located at one of a front and a back of thecombination stencil printer and dispenser and a non-print position inwhich the stencil is located at the other of the front and the back ofthe combination stencil printer and dispenser. The combination stencilprinter and dispenser further includes a substrate support coupled tothe frame to support a substrate in a print position and a print headcoupled to the frame to deposit and print viscous material over thestencil. The print head is configured to move across the stencil. Thecombination stencil printer and dispenser further includes a dispensercoupled to the stencil shuttle to dispense viscous material on thesubstrate when the substrate is in the print position.

Embodiments of the combination stencil printer and dispenser include abracket mounted on the stencil shuttle, and a dispensing unit supportedby the bracket. The bracket of the dispenser is coupled to a dispensermovement mechanism to move the dispenser with respect to the stencilshuttle in a second direction that is perpendicular to the firstdirection. The dispenser movement mechanism includes a linear bearingmounted on the stencil shuttle, the bracket being configured to ridealong the linear bearing. The dispenser movement mechanism furtherincludes a ball screw coupled to the bracket and configured to drive themovement of the bracket along the linear bearing. The dispenser movementmechanism further includes a motor coupled to the ball screw andconfigured to drive the rotation of the ball screw. The dispenserincludes another dispensing unit supported by the bracket. The stencilshuttle includes a pair of rail members secured to the frame and a drivemechanism coupled to the stencil shuttle.

A further aspect of the disclosure is directed to a method of depositingviscous material on a substrate, the method comprising: positioning thesubstrate in a print position; performing a print operation on thesubstrate with a print head and a stencil to deposit viscous material onthe substrate; and depositing viscous material on the substrate with adispenser attached to a stencil shuttle configured to support thestencil.

Embodiments of the method include imaging fiducials associated with thesubstrate and aligning the substrate with the stencil when positioningthe substrate in the print position. The method further includesdelivering the substrate to the substrate support prior to positioningthe substrate in the print position, cleaning a bottom surface of thestencil with a cleaning assembly, and/or inspecting the substrate with avision system to detect a defect with the deposit of viscous material onthe substrate. Inspecting the substrate with the vision system includesmoving the vision system over the substrate with a vision system gantryunder the control of a controller. Depositing viscous material on thesubstrate with the dispenser is performed after inspecting the substratewith the vision system to detect a defect. The dispenser is configuredto fix the defect.

One more aspect of the disclosure is directed to a combination stencilprinter and dispenser including a frame, a stencil coupled to the frame,a substrate support coupled to the frame to support a substrate in aprint position, a print head coupled to the frame to deposit and printviscous material over the stencil, and an independent gantry coupled tothe frame. The gantry is configured to move in a first direction. Thecombination stencil printer and dispenser further includes a dispensercoupled to the independent gantry to dispense viscous material on thesubstrate when the substrate is in the print position.

Embodiments of the combination stencil printer and dispenser includeproviding a bracket on a frame member of the independent gantry and adispensing unit supported by the bracket. The bracket of the dispenseris coupled to a dispenser movement mechanism to move the dispenser withrespect to the frame member of the independent gantry in a seconddirection that is perpendicular to the first direction. The dispensermovement mechanism includes a linear bearing mounted on the frame memberof the independent gantry with the bracket being configured to ridealong the linear bearing. The dispenser movement mechanism furtherincludes a ball screw coupled to the bracket and configured to drive themovement of the bracket along the linear bearing. The dispenser movementmechanism further includes a motor coupled to the ball screw andconfigured to drive the rotation of the ball screw. The movementmechanism of the independent gantry includes a pair of rail memberssecured to the frame and a drive mechanism.

A further aspect of the disclosure is directed to a method comprising:positioning the substrate in a print position; performing a printoperation on the substrate with a print head and a stencil to depositviscous material on the substrate; and depositing viscous material onthe substrate with a dispenser attached to an independent gantry of thecombination stencil printer and dispenser.

Another aspect of the present disclosure is directed to a method ofdepositing viscous material on a substrate with a combination stencilprinter and dispenser. The method comprises: positioning the substratein a print position; performing a print operation on the substrate witha print head and a stencil to deposit viscous material on the substrate;and inspecting the substrate with a vision system to detect a defectwith the deposit of viscous material on the substrate. In oneembodiment, the method further includes, in the event of a defect,re-working the substrate by depositing viscous material on the substratewith a dispenser attached to a cleaning assembly to correct the defect.In another embodiment, the method further includes, in the event of adefect, re-working the substrate by depositing viscous material on thesubstrate with a dispenser attached to a stencil shuttle to correct thedefect. In yet another embodiment, in the event of a defect, re-workingthe substrate by depositing viscous material on the substrate with adispenser attached to an independent gantry to correct the defect.

The present disclosure will be more fully understood after a review ofthe following figures, detailed description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a front perspective view of a combination stencil printer anddispenser of an embodiment of the disclosure;

FIG. 2 is a top perspective view of a dispenser and a stencil cleaningassembly of the stencil printer;

FIG. 3 is a bottom perspective view of the dispenser and the stencilcleaning assembly;

FIG. 4 is an outside partial cross-sectional right side view of a y-axismovement mechanism of the stencil cleaning assembly that is movablewithin the combination stencil printer and dispenser;

FIG. 5 is an inside perspective view of the y-axis movement mechanism;

FIGS. 6 and 7 are enlarged perspective views of the dispenser and anx-axis movement mechanism configured to move the dispenser;

FIG. 8 is an enlarged bottom perspective view of the dispenser and thex-axis movement mechanism;

FIG. 9 is an enlarged top perspective view of the dispenser and thex-axis movement mechanism;

FIG. 10 is a front perspective view of a combination stencil printer anddispenser of another embodiment of the disclosure; and

FIG. 11 is an enlarged perspective view showing a dispenser mounted on amovement mechanism.

DETAILED DESCRIPTION OF THE INVENTION

This disclosure is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The disclosure iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” “having,” “containing,”“involving,” and variations thereof herein, is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems.

The present disclosure relates generally to material applicationmachines, such as stencil printers, which may otherwise be referred toas “screen printers,” “printing machines” or “printers.” The presentdisclosure further relates to dispensers, such as traditional dispensersemploying auger screw dispensers or dispensers employing a devicecapable of jetting material (otherwise referred to as “jetters”), andother equipment utilized in surface mount technology (“SMT”) processlines. Such equipment may be configured to apply an assembly material(e.g., solder paste, conductive ink, or encapsulation material) onto asubstrate (e.g., a printed circuit board, referred to herein as an“electronic substrate,” a “circuit board,” a “board,” a “PCB,” a “PCBsubstrate,” a “substrate,” or a “PCB board”) or to perform otheroperations, such as inspection, rework, or placement of electroniccomponents onto a substrate.

In one example, a combination stencil printer and dispenser may beconfigured to perform a print operation and a dispense operation.Specifically, in a particular embodiment, the unit may include acombination stencil printer and dispenser that enables the operator toprint an assembly material onto a circuit board at a print station, andrepair poorly printed boards at the stencil printing station rather thana separate rework station. When a defect is detected on a board, and theboard is identified as being defective after inspection, the board maybe reworked directly within the same machine rather than being removedfrom the machine where the defect was discovered. In addition, inanother embodiment, such a combination stencil printer and dispenser maybe used to dispense a secondary material, such as adhesive, on theprinted circuit board at the stencil printing station. The dispenser maybe further configured to dispense large quantities of paste forlarge-part soldering.

In order to facilitate a reduction in space taken up by a productionline, or complexity of accessing a board within a printing machine, andto facilitate a reduction in interruptions of the process line andtherefore greater efficiency, some embodiments disclosed herein includeproviding other components in the combination stencil printer anddispenser.

Exemplary platforms, which may be modified to perform print and dispenseoperations in accordance with the methods disclosed herein, may include,but are not limited to the ACCELA® and MOMENTUM™ stencil printersoffered by Speedline Technologies, Inc. of Franklin, Mass., the assigneeof the present disclosure.

FIG. 1 shows a front perspective view of a combination stencil printerand dispenser, generally indicated at 100, in accordance with oneembodiment of the disclosure. The combination stencil printer anddispenser 100, which is sometimes referred to herein simply as a“combination printer,” may be configured from a MOMENTUM stencil printerplatform identified above. The combination printer 100 includes a frame102 that supports components of the combination printer, including butnot limited to a controller 104 located in a cabinet 106 of thecombination printer, a stencil 108, and a dispensing head, generallyindicated at 110, for dispensing a viscous material, such as solderpaste. The stencil 108 has apertures (not shown) through which viscousmaterial is deposited on the surface of a circuit board, such as circuitboard 112 shown in FIG. 1. The dispensing head 110 may be movable alongorthogonal axes by a gantry system (not designated) under the control ofthe controller 104 to allow printing of the viscous material on thecircuit board, which, as mentioned above, may sometimes be referred toas an electronic substrate. A cover 114 is shown in an open position toreveal the internal components of the combination printer 100.

Circuit boards 112 that are fed into the combination printer 100typically have a pattern of pads or other, usually conductive surfaceareas onto which viscous material will be deposited. The combinationprinter 100 also includes a conveyor system having rails 116, 118 fortransporting the circuit board 112 in an x-axis direction to a printingposition in the combination printer. Such a transport system includingrails 116, 118 is sometimes referred to as a “tractor feed mechanism.”In some implementations, the combination printer 100 has a supportassembly 120, e.g., pins, gel membranes, etc., positioned beneath thecircuit board 112 when the circuit board is in the print position. Thesupport assembly 120 may be used to raise the circuit board 112 off ofthe rails 116, 118 to place the circuit board in contact with, or inclose proximity to, the stencil 108 when printing (i.e., solder pastedepositing) is to occur. When directed by the controller 104 of thecombination printer 100, the tractor feed mechanism supplies boards to alocation over the support assembly 120 and under the stencil 108. Oncearriving at the position under the stencil 108, the circuit board 112 isin place for a manufacturing operation.

In one embodiment, the dispensing head 110 may be configured to receiveat least one solder paste cartridge (not shown) that provides theviscous material, such as solder paste, to the dispensing head during aprinting operation. In one embodiment, the solder paste cartridge iscoupled to one end of a pneumatic air hose in a well-known manner. Theother end of the pneumatic air hose may be attached to a compressorcontained within the frame 102 of the combination printer 100 that,under the control of the controller, provides pressurized air to thecartridge to force solder paste into the dispensing head 110 and ontothe stencil 108. Other configurations for dispensing solder paste ontothe stencil 108 may also be employed. For example, in other embodiments,mechanical devices, such as a piston, may be used in addition to, or inplace of, air pressure to force the solder paste from the cartridge intothe dispensing head 110. In yet another embodiment, the controller 104may be implemented using a personal computer having a suitable operatingsystem (e.g., Microsoft® DOS, Windows® NT, Windows Vista, UNIX, etc.)with application specific software to control the operation of thecombination printer 100 as described herein.

The combination printer 100 further includes a vision inspection system124 that is configured to move into position over the circuit board 112by a vision gantry 126 (FIG. 3) to align the circuit board delivered tothe print position and to inspect the solder paste deposits to determinewhether the solder paste has been accurately placed on the circuitboard. To successfully deposit solder paste on the circuit board 112,the circuit board and the stencil 108 are aligned, via the controller104. Alignment is accomplished by moving the stencil 108 or circuitboard 112 based on readings from the vision inspection system 124. Whenthe stencil 108 and the circuit board 112 are aligned correctly, thestencil is lowered toward the circuit board for application of thesolder paste through the apertures, or the circuit board can be raisedtoward the stencil by the support assembly 120. After the printoperation, inspection of the circuit board 112 aids in ensuring that theproper amount of viscous material has been deposited and that theviscous material has been deposited at the proper locations on thecircuit board. The vision inspection system 124 can use fiducials,chips, board apertures, chip edges, or other recognizable patterns onthe circuit board 112 to determine proper alignment. After inspection ofthe circuit board 112, the controller 104 controls movement of thecircuit board to the next location using the tractor feed mechanism,where electrical components may be placed on the circuit board.

In some embodiments, the combination printer 100 may operate as follows.The circuit board 112 may be loaded into the stencil printer 100 in aprint position using the conveyor rails 116, 118 and by aligning thecircuit board with the stencil 108. The dispensing head 110 may then belowered in the Z-direction until it is in contact with the stencil 108.The dispensing head 110 may fully traverse the stencil 108 in a firstprint stroke to force solder paste through apertures of the stencil andonto the circuit board 112. Once the dispensing head 110 has fullytraversed the stencil 108, the circuit board 112 may be transported bythe conveyor rails 116, 118 from the combination printer 1000 so that asecond, subsequent circuit board 112 may be loaded into the combinationprinter. To print on the second circuit board 112, the dispensing head110 may be moved in a second print stroke across the stencil in anopposite direction to that used for the first circuit board.

After one or more applications of the solder paste on the circuit boards112, excess viscous material may accumulate at the bottom of the stencil108. Referring to FIGS. 2 and 3, the combination stencil printer anddispenser 100 may be configured with a stencil wiper cleaning assembly,generally indicated at 128, which moves beneath the stencil 108 toremove the excess solder paste from the stencil. For the embodimentillustrated in FIGS. 1-9, the stencil wiper cleaning assembly 128 movesfrom a back of the combination printer 100 to a front of the combinationprinter in a y-axis direction to wipe excess material from the stencil108. In other embodiments, such as with the ACCELA stencil printeridentified above and described with reference to FIG. 10, a stencil maybe moved in the y-axis direction from a front of the stencil printer toa back of the stencil printer in which the stencil travels over astencil wiper cleaning assembly provided at the back of the stencilprinter. This particular embodiment of the combination printer thatmoves the stencil will be described in greater detail below.

Referring to FIGS. 2 and 3, as described above, the stencil wipercleaning assembly 128 is provided to wipe excess viscous material fromthe bottom surface of the stencil 108. With this embodiment, the stencilwiper cleaning assembly 128 is configured to move under the stencil 108to clean a bottom surface of the stencil. Removal of excess viscousmaterial, such as solder paste, can occur after each print cycle, orafter a number of print cycles when it has been determined that asubstantial amount of viscous material is on the surface of the stencil108 and should be removed. Additionally, before the circuit board 112can move to a next print operation in the combination printer 100 orotherwise, the circuit board is inspected to determine the accuracy withwhich viscous material has been deposited on the surface of the circuitboard.

As will be described in greater detail below with reference to FIGS. 4and 5, a y-axis movement mechanism or carriage is provided to drive they-axis movement of the stencil wiper cleaning assembly 128. As shown inFIGS. 2 and 3, the stencil wiper cleaning assembly 128 includes a frameassembly 130, which is configured to support the components of thestencil wiper cleaning assembly and is movable by the y-axis movementmechanism. The frame assembly 130 is configured to support a vacuumplenum 132, a paper supply that disposes paper over the vacuum plenum,and a solvent application device 134 to apply solvent on the paper. Inone embodiment, the paper supply includes a roll of paper housed on asupply roller 136, an idler shaft 138, a take-up roller 140 forreceiving the used paper, and a paper or web material driver 141 (FIG.3) for moving the paper across the stencil 108 in a linear directionfrom the supply roller to the take-up roller. It should be noted thatthe web of paper is not shown as it extends over the various componentsof the stencil wiper cleaning assembly 128 so as to more clearlyillustrate some of these components.

In one embodiment, the solvent application device 134 includes a solventroller that rotates within a bath of solvent to apply solvent onto thepaper as the paper moves between the supply roller 136 and the take-uproller 140. In other embodiments, the solvent application device 134includes a hollow solvent tube with numerous small openings formed alongthe length of the tube. The vacuum plenum 132 includes a wiper blade forremoving excess solvent and hardened solder paste from the paper as ittravels underneath the stencil 108. The vacuum plenum 132 is capable ofmoving the paper between a first position in which the paper is spacedaway from the stencil 108 and a second position in which the paperengages the stencil to wipe and draw excess material from the stencilonto the paper.

During a cleaning operation, the paper driver rotates the paper supplyroller 136 by driving the rotation of the take-up roller 140, whichpasses paper over the solvent roller 134 to wet the paper prior to theengagement of the paper to the stencil 108. The solvent impregnatedpaper is passed to the vacuum plenum 132, which holds the paper in placeas the stencil wiper cleaning assembly 128 moves under the stencil 108,thereby cleaning the stencil. The vacuum plenum 132 is operable toselectively engage the stencil 108 with the paper being disposed betweenthe vacuum plenum and the stencil. Excess solder paste is wiped off thestencil 108 as the vacuum plenum 132 engages and moves along a length ofthe stencil with the vacuum plenum drawing excess material from thestencil. As illustrated in FIG. 3, the stencil wiper cleaning assemblyfurther includes a belly pan 142 to contain excess solder and solventnot captured on the paper during a stencil wipe procedure to protectcomponents of the combination printer 100 and to prevent suchcontaminants from being deposited on the printed circuit board 112.

In certain embodiments, the operation of the stencil wiper cleaningassembly 128, including the operation of the vacuum plenum 132 and thepaper supply is described in detail in the following references: U.S.Pat. No. 6,955,121, entitled METHODS AND APPARATUS FOR CLEANING ASTENCIL; U.S. Pat. No. 7,017,489, entitled METHODS AND APPARATUS FORCHANGING WEB MATERIAL IN A STENCIL PRINTER; and U.S. Pat. No. 7,040,228,entitled SELF-CONTAINED VACUUM MODULE FOR STENCIL WIPER ASSEMBLY, all ofwhich are assigned to Speedline Technologies, Inc. of Franklin, Mass.,and incorporated herein by reference in their entirety for all purposes.

Turning now to FIGS. 4 and 5, the stencil wiper assembly is mounted on apair of rails and situated at one end (e.g., the back) of thecombination printer 100. As will be discussed with reference to thecombination printer illustrated in FIG. 10, the stencil wiper cleaningassembly may also stay stationary as the stencil is moved over theassembly to perform the cleaning operation. As discussed above, thecomponents of the stencil wiper cleaning assembly 128 including theframe assembly 130 are coupled to a y-axis movement mechanism, generallyindicated at 144, which is in turn coupled to the frame 102.Specifically, for each side of the stencil wiper cleaning assembly 128,the frame assembly 130 of the stencil wiper cleaning assembly rides on alinear rail 148, on which the stencil wiper cleaning assembly is movedback and forth using a belt and pulley drive mechanism. Alternatively,rack and pinion, chain and pulley, or ball screw drive mechanisms may beused in place of the belt and pulley mechanism to drive the movement ofthe stencil wiper cleaning assembly 128. The belt and pulley drivemechanism includes a first pulley 150 that is suitably driven by a motor152, a second pulley 154, and a belt 156, which suitably drives themovement of the stencil wiper cleaning assembly 128. The belt and pulleydrive mechanism may further include a gear reducer 158 and a belttension adjuster 160. In the shown embodiment, a y-axis movementmechanism includes an interface plate 162 to couple the belt 156 to theframe assembly 130 of the stencil wiper cleaning assembly 128.

The arrangement is such that the stencil wiper cleaning assembly 128 ismoved along in the y-axis direction by the y-axis movement mechanism 144by controlling the operation of the motor 152. In one embodiment, thecontroller 104 may be programmed to control the operation of the y-axismovement mechanism 144. A cable carrier 164 is provided to protect thewires and cables controlling the operation of the y-axis movementmechanism 144.

In addition to the views of the stencil wiper cleaning assembly shown inFIGS. 2 and 3, reference can also be made to FIGS. 6-9, whichillustrates a dispenser, generally indicated at 170, to dispense viscousmaterial on the circuit board 112 when the circuit board is in thedispense position. As shown, the dispenser 170 is secured or otherwisecoupled to an x-axis movement mechanism, generally indicated at 172, tomove the dispenser back and forth in an x-axis direction with respect toa frame member 174 of the frame assembly 130 of the stencil wipercleaning assembly 128. Thus, it should be observed that the dispenser170 is capable of being positioned over the circuit board 112 at anylocation by manipulating the y-axis movement mechanism 144 and thex-axis movement mechanism 172, preferably under the control of thecontroller 104.

The components embodying the dispenser 170 will be discussed first. Thedispenser 170 illustrated throughout the drawings is a two unitdispenser capable of dispensing two different types of materials, ifdesired, or capable of dispensing the same material. As shown, thedispenser 170 includes a mounting block 176, two pump mount housings,each indicated at 178, which are each secured to the mounting block in aposition under the mounting block, and two dispensing units, eachindicated at 180, which are each supported by respective pump mounthousings. In the shown embodiment, each dispensing unit 180 may beconfigured with an auger pump having a dispensing needle or nozzle todispense viscous material onto the circuit board 112. Two separateviscous material supply cartridges, each indicated at 182, one for eachdispensing unit 180, are suitably coupled to the mounting block 176 andare configured to supply viscous material to their respective dispensingunit. In certain embodiments, each viscous material supply cartridge 182is configured to contain viscous material, such as solder paste,adhesive and the like, and includes a syringe and a sensor configured todetect insufficient viscous material in the syringe. Each viscousmaterial supply cartridge 182 is in fluid communication with itsrespective dispensing unit 180, which in turn is powered by a motor 184having an encoder. As shown, the motors 184 are supported by themounting block 176 on opposite ends of the mounting block.

Although the dispenser 170 illustrated throughout the drawings includestwo dispensing units 180, it should be understood that the dispenser maybe configured with any number of dispensing units, such as a singledispensing unit or three or more dispensing units, and still fall withinthe scope of the present embodiment. In addition, the dispenser 170 mayfurther include a board height sensor 186, which is configured to detecta distance of the printed circuit board 112 from the dispenser units180. Each dispensing unit 180 of the dispenser 170 may also beconfigured to move vertically in a z-axis direction by one of twomethods—using the support assembly 120 to raise and lower the circuitboard 112 and by using an air cylinder to push the dispensing units 180to dispense positions. The movement of the support assembly 120 and/orthe air cylinders may be performed by the controller 104.

As mentioned, the dispenser 170 is movable in the x-axis direction bythe x-axis drive mechanism 172, which includes a linear rail or bearingthat is mounted on the frame member 174 of the frame assembly 130 of thestencil wiper cleaning assembly 128. The mounting block 176 is securedto a bracket 190, which is configured to ride on the linear rail 188 toprovide movement in the x-axis direction. As best shown in FIGS. 3 and9, driving the movement of the dispenser 170 is a motor 192 mounted onthe frame assembly 130 of the stencil wiper cleaning assembly 128, whichdrives the rotation of a ball screw 194. The bracket 190 includes a nut(not shown) that receives the ball screw 194 to drive the movement ofthe dispenser 170 with respect to the stencil wiper cleaning assembly128 in the x-axis direction. As with the y-axis movement mechanism 144,any suitable drive mechanism may be selected for powering the movementof the dispenser in the x-axis direction. In one embodiment, thecontroller 104 is configured to control the movement of the dispenser inthe x-axis direction by the x-axis movement mechanism 172. Another cablecarrier 196 is provided to protect the wires and cables controlling theoperation of the x-axis movement mechanism 172.

In operation, the combination printer 100 is configured to perform astencil print operation on a printed circuit board 112 in the knownmanner. After printing, a dispense operation may also take place byusing the dispenser 170 provided on the stencil wiper cleaning assembly128. In one embodiment, a method of depositing viscous material on acircuit board 112 delivered to the combination printer 100 includesdelivering a circuit board to the combination printer, positioning thecircuit board in the print and dispense positions, performing a printoperation on the circuit board with the dispensing head 110 and thestencil 108 to deposit viscous material on the circuit board, anddepositing viscous material on the circuit board with the dispenser 170,which is attached to the stencil wiper cleaning assembly 128. Whenpositioning the circuit board 112 in the print position, the circuitboard is aligned with the stencil 108. When positioning the circuitboard 112 in the dispense position, the imaging system may be used todetect a fiducial on the circuit board to accurately dispense material.Once the printing and dispensing takes place, a bottom surface of thestencil 108 is cleaned with the stencil wiper cleaning assembly 128.Alternatively, or in addition to cleaning the stencil 108, the circuitboard 112 is inspected with the vision inspection system 124 to detect adefect with the deposit of viscous material on the circuit board. Wheninspecting, the vision gantry 126 is provided to move the visioninspection system 124 over the circuit board 112 under the control of acontroller 104.

In another embodiment, a method of depositing viscous material on asubstrate delivered to the combination printer 100 includes positioningthe circuit board 112 in the print position, performing a printoperation on the circuit board with the dispensing head 110 and thestencil 108 to deposit viscous material on the circuit board, inspectingthe circuit board with the vision inspection system 124 to detect adefect with the deposit of viscous material on the circuit board, and,in the event of a defect, re-working the circuit board by depositingviscous material on the circuit board the dispenser 170, which isattached to the cleaning assembly 128, to correct the defect.

Turning now to FIG. 10, a combination stencil printer and dispenser ofanother embodiment is generally indicated at 200. The combinationprinter 200 includes a frame 202, a controller 204, a movable stencil206, at least one solder paste cartridge 208, a dispensing head 210, acircuit board support assembly 212, and a tractor feed mechanism 214configured to transport a circuit board 216. The circuit board 216enters the combination printer 200 on the tractor feed mechanism 214.The movable stencil 206 includes a stencil shuttle 218, which supportsand moves the stencil 206 to a position above the circuit board 216 toperform a print operation on the circuit board when the circuit board isin the print position. The controller 204 is internal to the mechanismsof the combination printer 200, and is configured to receive signalsfrom operations in the combination printer, such as alignment of thecircuit board 216, movement of the movable stencil 206, and deposit ofthe viscous material, and control the printer accordingly.

A vision inspection system 220 is provided to align the circuit board216 and the movable stencil 206 and to inspect the circuit board afterthe print operation. When inspecting, the vision inspection system 220moves over the circuit board 216 by a vision gantry 222 to inspect theviscous material deposits to determine whether the viscous material hasbeen accurately placed on the circuit board. After inspection of thecircuit board 216, the controller 104 controls movement of the circuitboard 216 to the next location using the tractor feed mechanism 214,where electrical components will be placed on the circuit board. Inaddition to vision inspection of the circuit board 216 upon completionof the deposition of viscous material onto the circuit board, in oneembodiment of the disclosure, the movable stencil 206 is cleaned using astencil wiper (not shown) to remove excess solder paste from the surfaceof the movable stencil prior to beginning a print cycle on a nextcircuit board. Generally, as described above with reference to thecombination printer 100 shown and described in FIGS. 1-9, the stencilwiper of combination printer 200 used to clean the movable stencil 206.With the combination printer 200, the stencil wiper is positioned at arear of the combination printer to wipe the surface of the movablestencil 206 after printing has occurred and the movable stencil is movedto the rear of the combination printer.

Specifically, to accomplish improvements and efficiency in the printcycle, with the combination printer 200 the board inspection process andthe stencil cleaning process occur substantially in parallel. During theinspection of at least one of the circuit boards 216, the movablestencil 206 is moved to a position where a stencil wipe process occurs.In operation, after printing, the movable stencil 206 translates, forexample toward the back of the combination printer 200, to be cleaned.The movable stencil 206 can move by way of the stencil shuttle 218 in aforward and backward motion. The movable stencil 206 is cleaned bymoving from front to back over the stencil wiper, as the stencil wipercontacts the bottom surface of the movable stencil and removes excesssolder paste. The movable stencil 206 moves to the back and over thesurface of the stencil wiper by moving backward in the combinationprinter 200, and the movable stencil moves back into position by movingforward. This motion is the translation of the movable stencil 206 inthe y-axis direction, although it is possible that translation of themovable stencil in the combination printer 200 may occur in the x-axisdirection alternatively or additionally.

During the time in which the movable stencil 206 is cleaned by thestencil wiper, or substantially simultaneously, the vision inspectionsystem 220 moves into a position over the surface of the circuit board216 to perform an inspection task. The vision inspection system 220moves in a forward and back motion by way of the vision gantry 222, andis restricted in its movements to a position over the circuit board 216while the movable stencil 206 is being cleaned, since the movablestencil is moved toward the rear of the combination printer 200, therebyallowing a substantial space over the circuit board for the visioninspection system to inspect. Thus, wiping of the movable stencil 206and inspection of the circuit board 216 may be accomplished in parallel.

Upon completion of inspection, the circuit board 216 exits thecombination printer 200. The circuit board 216 can exit the combinationprinter 200 while the movable stencil 206 continues to be cleaned. Theprinting of a first circuit board 216 is thereby completed, and thecircuit board can continue to a next manufacturing cycle. Thecombination printer 200 is prepared to accept a new circuit board 216,and a next print cycle can begin. While the next circuit board 216 movesinto position in the combination printer 200, the stencil wipe processis completed and the movable stencil 206 moves towards the front of thecombination printer to begin the printing cycle for the new circuitboard.

In certain embodiments, the platform of the combination stencil printerand dispenser 200 shown and described with reference to FIG. 10 isdescribed in detail in the following references: U.S. Pat. No.7,013,802, entitled METHOD AND APPARATUS FOR SIMULTANEOUS INSPECTION ANDCLEANING OF A STENCIL; U.S. Pat. No. 7,272,898, entitled METHOD ANDAPPARATUS FOR PERFORMING OPERATIONS WITHIN A STENCIL PRINTER; U.S. Pat.No. 7,322,288, entitled METHOD AND APPARATUS FOR PERFORMING OPERATIONSWITHIN A STENCIL PRINTER; and U.S. Pat. No. 7,469,635, entitled METHODAND APPARATUS FOR PERFORMING OPERATIONS WITHIN A STENCIL PRINTER, all ofwhich are assigned to Speedline Technologies, Inc. of Franklin, Mass.,and incorporated herein by reference in their entirety for all purposes.

Still referring to FIG. 10, the combination printer 200 includes adispenser, generally indicated at 230, to dispense viscous material onthe circuit board 216 when the circuit board is in a dispense position.As shown, the dispenser 230 is secured or otherwise coupled to thestencil shuttle 218 of the movable stencil 206 and an x-axis movementmechanism, generally indicated at 232, is provided to move the dispenserback and forth in an x-axis direction with respect to a stencil shuttle.The construction of dispenser 230 and the x-axis movement mechanism 232are substantially identical in construction to the construction of thedispenser 170 and x-axis movement mechanism 172. The dispenser 230 ismovable in the x-axis direction by the x-axis drive mechanism 232, whichincludes a linear rail or bearing 234 that is mounted on the stencilshuttle 218. The dispenser 230 is configured to ride on the linear rail234 to provide movement in the x-axis direction. In one embodiment, thecontroller 204 is configured to control the movement of the dispenser230 in the x-axis direction by controlling the operation of the x-axismovement mechanism. Similarly, the controller 204 is configured tocontrol the movement of the dispenser 230 in the y-axis direction bycontrolling the operation of the stencil shuttle 218.

In operation, the combination printer 200 is configured to perform astencil print operation on a printed circuit board 216 when the movablestencil 206 is positioned over the circuit board. After printing, adispense operation may also take place by using the dispenser 230provided on the stencil shuttle 218. In one embodiment, a method ofdepositing viscous material on the circuit board 216 delivered to thecombination printer 200 includes delivering the circuit board to thecombination printer, positioning the circuit board in the printposition, if required, moving the movable stencil 206 over the circuitboard, performing a print operation on the circuit board with thedispensing head 210 and the movable stencil to deposit viscous materialon the circuit board, and depositing viscous material on the circuitboard with the dispenser 230, which is attached to the stencil shuttle218. When positioning the circuit board 216 in the print position, anddisposing the movable stencil 206 over the circuit board, the circuitboard is aligned with the movable stencil. Once the printing anddispensing takes place, a bottom surface of the movable stencil 206 maybe cleaned with the stencil wiper by moving the stencil over the stencilwiper.

In another embodiment, a method of depositing viscous material on asubstrate delivered to the combination printer 200 includes positioningthe circuit board 216 in the print position, performing a printoperation on the circuit board with the dispensing head 210 and themovable stencil 206 to deposit viscous material on the circuit board,inspecting the circuit board with the vision inspection system 220 todetect a defect with the deposit of viscous material on the circuitboard, and, in the event of a defect, re-working the substrate bydepositing viscous material on the substrate with the dispenser 230attached to the stencil shuttle 218 to correct the defect.

FIG. 11 illustrates a dispenser, generally indicated at 300, coupled toan x-axis movement mechanism, generally indicated at 302, which in turnis secured to an independent gantry 304. In this embodiment, theindependent gantry 304 may be provided in any type of stencil printer,including the ACCELA and MOMENTUM stencil printer platforms describedabove. The arrangement is such that the independent gantry 304 may beconfigured to move in the y-axis direction within the combinationstencil printer and dispenser.

As used herein, “print position” identifies a position in which thecircuit board is ready to be printed upon and/or dispensed upon. Forcombination printer 100, the print position is identified when thecircuit board 112 is delivered to the support assembly 120 and a printoperation can be performed on the circuit board. In this print position,a dispense operation with dispenser 170 may be performed as well. Assuch, the print position may be identified as the dispense position aswell. For combination printer 200, the print position is identified whenthe circuit board 216 is delivered to the support assembly 212 and themovable stencil 206 is positioned over the circuit board. In thisposition, a print operation and a dispense operation with dispenser 232may be performed on the circuit board 216.

Having thus described several aspects of at least one embodiment of thisdisclosure, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe disclosure. For example, the parameters described herein may bemodified to accommodate different printing process requirements.Accordingly, the foregoing description and drawings are by way ofexample only.

What is claimed is:
 1. A method of depositing viscous material on asubstrate with a combination stencil printer and dispenser, the methodcomprising: positioning the substrate in a print position; performing aprint operation on the substrate with a print head having a firstdispenser and a stencil to deposit viscous material on the substrate;inspecting the substrate with a vision system to detect a defect withthe deposit of viscous material on the substrate; and in the event of adefect, re-working the substrate by depositing viscous material on thesubstrate with a second dispenser provided in the stencil printer tocorrect the defect, wherein the second dispenser is directly attached toa cleaning assembly configured to move relative to the stencil and thesubstrate.
 2. The method of claim 1, wherein positioning the substratein the print position includes imaging fiducials associated with thesubstrate and aligning the substrate with the stencil.
 3. The method ofclaim 2, further comprising delivering the substrate to the substratesupport prior to positioning the substrate in the print position.
 4. Themethod of claim 1, further comprising cleaning a bottom surface of thestencil with the cleaning assembly.
 5. The method of claim 1, whereininspecting the substrate with the vision system includes moving thevision system over the substrate with a vision system gantry under thecontrol of a controller.